We classified resected intraductal papillary mucinous neoplasms (IPMNs) into four subtypes (gastric, intestinal, pancreatobiliary and oncocytic) according to their morphological features and mucin expression, determined their clinicopathological characteristics and investigated the possibility of preoperatively diagnosing these subtypes. Sixty resected tumors, 4 preoperative tumor biopsies and 10 preoperative pancreatic juice cytology specimens were analyzed. The gastric and intestinal types accounted for the majority of IPMNs. Non-gastric type IPMNs were of high-grade malignancy. Many of the pancreatobiliary-type IPMNs were in an advanced stage and were associated with a poor prognosis. The results of mucin immunohistochemical staining of preoperative biopsy and surgically resected specimens were in agreement with each other, and in close agreement with those for pancreatic juice cytology specimens obtained from 10 patients during endoscopic retrograde cholangiopancreatography (ERCP). The immunostaining of preoperative biopsy specimens and ERCP-obtained pancreatic juice cytology specimens may be useful in the differential diagnosis of gastric and intestinal types of IPMN. If such techniques enable the preoperative diagnosis of IPMN subtypes, their use in combination with conventional preoperative imaging modalities may lead to surgical treatment best suited for the biological characteristics of the four subtypes.